The obesity conundrum – obesity then infection or infection then obesity?

Introduction: Obesity is defined as an excess of body fat, and the fundamental causes are sedentary lifestyles, high-fat and energy-dense diets and the behavioural patterns of communities as a consequence of increased urbanization. Research on obese individuals has shown that they have impaired immune function, which increases their susceptibility to infection. Recently, research has found that various microbes, including gut microbiota, influenza H1N1 virus, adenovirus 36 and Toxoplasma gondii, increase adiposity in humans and that proliferating pre-adipocytes and immune cells share an embryonic origin, which explains the link between obesity and infections. Aim and objectives: The aim of this literature review was to search the scientific literature to ascertain the association between obesity and infectious diseases and to analyse which is a more serious issue – obesity predisposing people to infections or infections leading to obesity. Material and methods: Google, Google Scholar, PubMed and the Journal of Obesity were the research repositories searched for relevant studies using the keywords infectious diseases, microbes and obesity. The research studies were reviewed and the results presented. Results: Through our review we found that the agents that most strongly predisposed people to obesity were adenovirus 36 and 37, T. gondii and Enterobacter, which led to obesity in 30% of adults. A vast majority of micro-organisms, such as influenza H1N1 virus, Candida albicans, Mycobacterium tuberculosis, coxsackievirus and Helicobacter pylori, were found to cause diseases in obese individuals. Conclusion: A review of the current studies does not conclusively prove that infections lead to obesity, with the exception of adenovirus 36; however, it does prove that obese people are prone to infections through an interplay of different mechanisms. Further research is required to establish the eminence of one over the other.